DESCRIPTION

Each of these functions has the same behaviour as its counterpart
without the `_unlocked' suffix, except that they do not use locking
(they do not set locks themselves, and do not test for the presence
of locks set by others) and hence are thread-unsafe.
See
flockfile(3).

CONFORMING TO

The four functions fIgetc_unlockedfP(), fIgetchar_unlockedfP(),
fIputc_unlockedfP(), fIputchar_unlockedfP() are in POSIX.1.
The nonstandard
*_unlocked()
variants occur on a few Unix systems, and are available in recent glibc.
They should probably not be used.